"I just fired the head of the F.B.I. He was crazy, a real nut job," The New York Times reported Trump as saying, citing written records of the meeting.

“I faced great pressure because of Russia. That’s taken off,” he added.

If true, the revelations would add growing momentum to scrutiny about Trump's firing of Comey. Allegations have been steadily building that Trump fired Comey because of the FBI's investigation into possible collusion between the Trump campaign and Russia's efforts to influence last year's presidential race.

The president has insisted he was acting in the best interests of the bureau and was motivated by Comey's handling of the Hillary Clinton email scandal.

White House spokesman Sean Spicer did not refute the latest reported comments, instead said Trump "has always emphasized the importance of making deals with Russia.

"By grandstanding and politicizing the investigation into Russia's actions, James Comey created unnecessary pressure on our ability to engage and negotiate with Russia," Spicer said in a statement.

“The investigation would have always continued, and obviously, the termination of Comey would not have ended it. Once again, the real story is that our national security has been undermined by the leaking of private and highly classified conversations,” he added.